Telephone call monitoring systems are used in a variety of contexts, including emergency dispatch centers and commercial call centers. In many currently available call monitoring systems, a multitude of audio input sources ("channels") are monitored and recorded by a single hardware unit, and the audio recordings are saved and organized according to the input channel, date, time and duration. The capacity of the recording unit can be expanded to handle a larger number of channels by combining several recording units into a system using a local area network (LAN). Because retrieval is only possible using basic search criteria (recording unit, channel, date, time and duration), it is often difficult to locate a particular audio recording that is of interest. When there is a need to search for a recording according to search criteria that are not directly supported by simple voice recording, locating a specific recording may require tedious and repetitive searching. For example, if there is a need to find a specific customer's call to resolve a disputed transaction, the recording unit or channel that carried the original call might not be known, so the searcher would be forced to manually play back many calls before finding the correct one.
With the advent of computer telephony integration (CTI), it is now possible to monitor a data link that supplies more information about telephone calls, in addition to simple voice recording. In a typical CTI system a telephone switch or private branch exchange (PBX) provides an interface suitable for processing by a computer, and expanded information about telephone calls is made available through this interface as the calls occur. Data fields that are available within this expanded information may include the external telephone number of the calling party, as well as identification numbers to help associate a series of events pertaining to the same call. With such a data link being used alongside a voice recording system, the search and retrieval system can be supplemented by constructing a database that combines the previously discussed basic search criteria with enhanced search criteria (based upon information obtained through a CTI data link) such as: telephone numbers of parties involved in the call; Caller ID (CLID) or Automatic Number Identification (ANI); Dialed Number Identification Service (DNIS); or the Agent ID Number of the Customer Service Representative.
As shown in FIG. 2, with suitable equipment for tapping into a voice communications line, a recording unit can intercept telephone call traffic using two methods. By attaching wires for recording channels on each extension within a call center, the traffic can be intercepted and recorded as it passes between the PBX and the agent telephone set. This first method is known as "station-side" recording 180. Alternatively, by attaching equipment on the trunk lines between the PBX and Public Switched Telephone Network (PSTN), the traffic can be intercepted at its point of entry into the call center before the calls are dispatched by the PBX. This second method is known as "trunk-side" recording 170. Since businesses usually have more agent telephone sets than trunk lines, a "trunk-side" solution is likely to require less recording equipment and thus be less expensive. Another significant point for consideration is that "trunk-side" provides access only to external inbound or outbound calls, which are those typically involving customers of a business, whereas "station-side" also provides access to internal calls between agents (which may or may not relate to an external customer's transaction).
With respect to data links to provide call information to computers, there are typically two different categories of links from the PBX available. Some older links use interfaces such as SMDR (Station Message Detail Recording) or CDR (Call Detail Recording) that provide summary information about telephone calls in a line-oriented text format. Both acronyms refer to essentially the same type of system. Information from these links is generally provided after the call has concluded, and as such is suitable for billing applications or traffic analysis software. Many newer links use real-time interfaces that are designed to supply a series of events while a telephone call is still active within the PBX, to enable computer and multimedia systems to respond and interact with an external caller. The information provided by such real-time links is typically much more detailed than that provided by SMDR.
The detailed information and real-time nature of a CTI link is particularly important hen building a recording system that is intended to react to telephone calls as they occur and to dynamically select which calls ought to be recorded or discarded. CTI-supplied information is also important when building a recording system that is intended to capture the full history of a telephone call, including recording the different agents who were involved in the conversation and how the call was held, transferred or conferenced. Likewise, real-time information is important in a system that intends to support (a) a live display of active calls, and (b) the capability for a user to listen and monitor the live audio traffic.
A "trunk-side" solution based upon voice recording alone will not satisfy the above requirements in a practical manner, since telephone calls are assigned to trunks dynamically as needed to handle the traffic. What trunk channel a particular call will be carried on cannot be predicted in advance. Without information to associate a logical telephone call with a physical recording of audio from a trunk channel, a user might have to search and retrieve many recordings before finding the one that is of interest. Moreover, in a system designed to make use of the enhanced search criteria provided by a data link, it would not be possible to programmatically associate the search data with the voice recording without information about the trunk channel where the call occurred.
This problem can be avoided as long as the data link provides sufficient information about the trunk channels being used for each call. Unfortunately, some PBX environments do not supply this critical information about trunk channels within the data provided on the real-time CTI link. For example, this problem is manifested by the Lucent Technologies DEFINITY G3 PBX, which is a commonly used telephone switch in North America. While the Lucent G3 PBX provides trunk channel information through its SMDR link, that information is not available until after the conclusion of the call. This presents a problem for system features and capabilities dependent upon real-time data. The real-time data link provided by the Lucent G3 PBX does not provide the necessary information about trunk channels. There is thus a need for a system which is capable of simultaneously monitoring both the SMDR link and the real-time CTI link, gathering information about calls from both sources, and combining that information into a single data model of the telephony activity within the call center. There is a further need for a system that combines the data model with information concerning the location of call recordings, resulting in a "master call record" that contains data matching each call with the segments of which it is comprised, and matching the data for each segment with the location of the recording of that segment. Such a system would facilitate monitoring, recording, and playing back complete telephone calls. There is also a need for a system capable of playing back telephone call segments stored at different locations and assigned to different playback servers in the order in which the segments occurred and without any perceptible time lag between played back segments. Such a system would enable a user to play back a complete telephone call and hear the call the way an outside caller would hear it as it occurred.